1. Field of the Invention
This invention relates to an apparatus for use in welding of a seat back frame for a reclining seat having locking mechanisms provided at lower portions of both side frame sections of the seat back frame for locking a seat back relative to a seat cushion and, more particularly, to an apparatus which is employed when a supporting shaft of a substantially cylindrical shape which is to interconnect the locking mechanisms is welded to one of the locking mechanisms.
2. Description of Related Art
Generally, as a reclining seat for an automotive vehicle, there is employed a seat that is provided at pivotal portions between a seat back and a seat cushion with locking mechanisms for locking the seat back relative to the seat cushion.
Referring to FIG. 23, there is illustrated the conventional seat which is provided with the locking mechanisms and is an assistant seat (companion seat) for an automotive vehicle having a steering wheel at the right side. The locking mechanisms 1, 1′ that are constructed in the same manner are provided at pivotal portions between side frame sections 2a, 2b of a seat back frame 2 and brackets 3a, 3b of a seat cushion frame (not shown). A supporting shaft 4 of a substantially cylindrical shape interconnects the locking mechanisms 1, 1′. An operating lever 5 is provided at the locking mechanism 1 which is arranged at the left side of a passenger sitting on the seat (adjacent a door of the automotive vehicle (at the right side in FIG. 23)).
Referring to FIG. 24, spiral springs 6 (only one spiral spring 6 is shown in FIG. 24) are stretched between the side frame sections 2a, 2b and the brackets 3a, 3b. A coil spring 7 is stretched between the operating lever 5 and the bracket 3a. In the seat constructed as mentioned above, when the locking mechanisms are synchronously unlocked by operating the operating lever 5, a seat back of the seat can be reclined relative to a seat cushion of the seat, or can be returned to an original state, and a posture of the seat back relative to the seat cushion can be changed by adjusting an angle of the seat back relative to the seat cushion.
As each of the locking mechanisms, there is employed a locking mechanism which comprises a disk-like housing, a disk-like cover plate including an annular wall having gear teeth formed on an inner surface thereof, the housing and cover plate being combined with each other in a face-to-face relation so as to be rotatable relative to each other, locking gears provided at regions of peripheries thereof with gear teeth which are adapted to be meshed with the gear teeth of the cover plate, and a cam for causing the locking gears to be releasably meshed with the gear teeth of the cover plate, the locking gears and the cam being arranged between the housing and the cover plate (for example, French Patent No. 2,578,602, Japanese patent application laid open under Provisionary Publication No. Hei. 8-253063 and U.S. Pat. No. 6,312,053).
Referring now to FIG. 25, as one example of the locking mechanisms, there is illustrated a concrete construction of the locking mechanism 1 arranged at the left side. The locking mechanism 1 comprises a disk-like housing 10, a disk-like cover plate having gear teeth provided around an inner surface of an annular wall thereof, locking gears 12, 13, 14 having gear teeth 12b, 13b, 14b provided at regions of peripheries thereof, a round bar-like actuating shaft 16, and a cam 15 for causing the locking gears 12-14 to be displaced, the cam being mounted on the actuating shaft 16. The locking mechanism 1 further includes spiral springs 17a, 17b, 17c for urging and supporting the cam 15, a guide pate 18 for inducting the locking gears 12-14 and causing the locking gears 12-14 to be displaced, a ring-like cover 19 for holding the housing 10 and the cover plate 11 while maintaining the housing 10 and the cover plate in a face-to-face relation.
The locking mechanisms 1, 1′ are provided at the pivotal portions between the seat back and the seat cushion by causing the housings 10 to be secured to the brackets 3a, 3b of the seat cushion frame, and causing the cover plates 11 to be secured to the side frame sections 2a, 2b of the seat back frame. A supporting shaft 4 is interconnects the actuating shafts 16 of the locking mechanisms 1, 1′.
When the locking mechanisms 1, 1′ are mounted to lower portions of the side frame sections 2a, 2b, the round bar-like actuating shafts 16, 16 are penetrated through the side frame sections 2a, 2b, projected inwardly from the side frame sections 2a, 2b so as to be aligned with each other, fitted in both end portions of the supporting shaft 4 and rigidly welded to the both end portions of the supporting shaft 4.
In the conventional seat in which the supporting shaft 4 is rigidly welded at the both end portions thereof to the actuating shafts 16, 16, when the passenger having sat on the seat operates the operating lever or the passenger causes the seat back to be returned to a condition where the passenger can sit on the seat, if any force which tends to cause the supporting shaft to be twisted is applied to the supporting shaft, there is a possibility that the cams of the locking mechanisms will not be synchronously actuated and will be actuated differentially from each other. Therefore, the locking gears of one of the locking mechanisms are normally meshed with the gear teeth of a corresponding cover plate, whereas the locking gear of the other of the locking mechanisms may not be normally meshed with the gear teeth of a corresponding cover plate. This results in a situation in which an angle of the seat back relative to the seat cushion can not be smoothly adjusted in such a manner that the passenger is allowed to sit on the seat.
In order to prevent the differential actuation of the cams, it is proposed that one end portion of the supporting shaft is coupled to the actuating shaft of one of the locking mechanisms so as to be rotatable relative to the actuating shaft of the one of the locking mechanisms at an angle of a few degrees. In this case, even if any force which tends to cause the supporting shaft to be twisted is applied to the supporting shaft, the cams of the locking mechanisms are not actuated differentially from each other, and the locking gears of the locking mechanisms are kept normally engaged with the gear teeth of the corresponding cover plates, so that the seat back can be smoothly reclined relative to the seat cushion.
Referring now to FIG. 26 illustrating the concrete connecting construction of the supporting shaft and the actuating shaft 16′ of the one of the locking mechanisms, the one end portion 4b of the supporting shaft 4 is deformed in a substantially elliptic shape in cross-section, and one end portion of the actuating shaft 16′ is deformed in such a manner that the actuating shaft 16′ is allowed to be rotatable relative to the supporting shaft 4 at an angle of a few degrees in a condition where the one end portion of the actuating shaft 16′ is coupled to the one end portion 4b of the supporting shaft 4. The one end portion 4b of the supporting shaft 4 and the actuating shaft 16′ are coupled to each other in such a manner that they become engaged with each other at a rotation starting point of the operating lever (the operating lever is adapted to be rotated in such a direction as to be indicated by an arrow in FIG. 26). The other end portion of the supporting shaft 4 is rigidly connected to the actuating shaft 16 of the other of the locking mechanisms by welding.
In this construction, when the operating lever is to be rotated by the passenger, the one end portion of the supporting shaft 4 and the actuating shaft 16′ are in the engaged condition, so that the both locking mechanisms can be synchronously actuated at the instant.
Furthermore, the one end portion of the supporting shaft 4 is coupled to the actuating shaft 16′ of the locking mechanism so as to be rotatable relative to the actuating shaft 16′ at the angle of a few degrees, so that when any force which tends to cause the supporting shaft 4 to be twisted is applied to the supporting shaft 4, the supporting shaft 4 is rotated relative to the actuating shaft 16′. Therefore, any force which tends to cause the cams of the both locking mechanisms to be actuated differentially from each other is not applied to the both locking mechanisms, and the locking gears of the both locking mechanisms can be kept normally meshed with the gear teeth of the corresponding cover plates.
As discussed above, the supporting shaft is merely fitted at the both end portions thereof on the actuating shafts which project inwardly from the side frame sections so as to be aligned with each other when the locking mechanisms are mounted to the lower portions of the side frame sections. In this condition, the deformed one end portion 4b of the supporting shaft 4 may not always be normally engaged with the deformed one end portion of the actuating shaft 16′. Therefore, when the other end portion of the supporting shaft is to be welded to the actuating shaft 16, it is necessary to adjust an angular deviation of the one end portion 4b of the supporting shaft 4 relative to the actuating shaft 16′ in such a manner that the one end portion 4b of the supporting shaft 4 is previously engaged with the actuating shaft 16′ at the rotation starting point of the operating lever.
The engagement of the one end portion 4b of the supporting shaft 4 with the actuating shaft 16′ may be performed by causing the supporting shaft 4 to be rotated relative to the actuating shaft 16′ by hand. However, when the other end portion of the supporting shaft is to be welded to the actuating shaft 16, a worker must weld the other end portion of the supporting shaft to the actuating shaft 16 while gripping the supporting shaft so as not to cause the supporting shaft to be shifted relative to the actuating shaft 16′. This is very troublesome.